A printing system for printing using two colorants, black plus a highlight color, and more specifically a printing system which has stored in memory a number of ink fonts, each of these fonts a different shade of highlight color, the members of each font being a large number of shapes which can be assembled to form rectangles of any size from which the highlight areas can be assembled.
To add highlight color to a typical black and white print, a xerographic printer can be designed with a tri-level development process. The photoconductor is charged in the form of an image where some areas are charged positively and some areas are charged negatively relative to non-image areas. Then, by using black toner with a positive potential and color toner with a negative potential, both black text and colored highlight areas can be printed on the same print in one pass. These highlight areas can be regular shapes such as a colored borders or highlighted areas of the page, or more complex shapes such as a rough approximations of flowers, or other figures.
The highlight colorant is typically red, green or blue. Then, the printer, at any given moment, will have black toner and one toner of one of these three colors. It is left to the user to load any color, and to change to another color at any time by removing the original toner cartridge and inserting another.
Toners are usually applied to paper to achieve variations of density by halftoning. In this embodiment, the halftone matrix will be assumed to be 8 by 8 pixels, each pixel being either white, black or colored. The resultant variations with red highlight and black toner can vary from white, light pink and light gray to red or black, and to any mixture of these.
Most printers typically print characters, and therefore the hardware is optimized for the storage, accessing and printing of alphabetical or numerical character bit maps. Substituting a tri-level development process, it would be relatively simple to print text in black or in a high light color. However, the requirement for producing arbitrary shapes in varying shades of color would complicate the hardware and software and impact run time. When the printer receives an instruction to print a specified color in a specified shape, it must define the area in the page bit map, produce a halftoned tile in the desired color, and then load the area with these tiles, all before printing can start. Clearly, this will impact unit cost and run time. What would be an improvement would be a printing system where arbitrary shapes and colors can be printed with equipment that was originally optimized to print text.